A number of ultrasonic devices have heretofore been proposed for use in ablating or removing obstructive material from blood vessels. Examples of devices which purportedly utilize ultrasonic energy, alone or in conjunction with other treatment modalities, to remove obstructions from blood vessels include those described in U.S. Pat. Nos. 3,433,226 (Boyd), 3,823,717 (Pohlman, et al.), 4,808,153 (Parisi), 4,936,281 (Stasz), 3,565,062 (Kuris), 4,924,863 (Sterzer), 4,870,953 (Don Michael, et al.), 4,920,954 (Alliger, et al.), and 5,100,423 (Fearnot) as well as other patent publications W087-05739 (Cooper), W089-06515 (Bernstein, et al.), W090-0130 (Sonic Needle Corp.), EP316789 (Don Michael, et al.), DE3,821,836 (Schubert) and DE2,438,648 (Pohlman).
Ultrasound transmitting catheters have been utilized to successfully ablate various types of obstructions from blood vessels of humans and animals. Particular success has been observed in ablation of obstructions located in peripheral blood vessels such as the femoral arteries. Successful applications of ultrasonic energy to smaller blood vessels, such as the coronary arteries, necessitates the use of relatively small diameter ultrasound transmitting catheters which are sufficiently small and flexible to undergo transluminal advancement through the tortuous vasculature of the aortic arch and coronary tree. Because of its small diameter, the ultrasound transmission member which extends through such catheters is particularly susceptible to breakage.
Additionally, ultrasound transmitting catheters may be utilized to deliver ultrasonic energy to blood vessel walls for the purpose of preventing or reversing vasospasm as described in copending U.S. patent application Ser. No. 07/911,651, entitled ANGIOPLASTY AND ABLATIVE DEVICES HAVING ONBOARD ULTRASOUND COMPONENTS AND DEVICES AND METHODS FOR UTILIZING ULTRASOUND TO TREAT OR PREVENT VASOSPASM. The ultrasound transmission member of such catheters are also susceptible to breakage.
As those skilled in the art will appreciate, breakage of ultrasound transmission members typically occurs near the proximal end thereof, generally within a few ultrasound nodes of the interface of the ultrasound catheter coupling and the ultrasound transducer coupling. This is believed to be because energy concentrations are highest at these points. Thus, any external forces applied to the ultrasound transmission member in this region may result in stresses exceeding the elastic limit of the ultrasound transmission member.
External forces may be inadvertently and undesirably applied to the ultrasound transmission member by pressing upon or bumping the ultrasound transmission member coupling during use of the ultrasound catheter. Such pressing upon or bumping of the ultrasound catheter coupling results in bending or other movement thereof which causes the inner wall thereof to contact the ultrasound transmission member. Such contacting of the ultrasound transmission member by the inner wall of the ultrasound catheter coupling applies forces, i.e., frictional and/or bending, thereto. If ultrasound energy is being transmitted by the ultrasound transmission member at the instant such forces are applied thereto, stresses occur which commonly result in breakage of the ultrasound transmission member.
As such, it would be beneficial to provide a means for mitigating the occurrence of ultrasound transmission member breakage by reducing mechanical stress applied to the proximal end of the ultrasound transmission member during operation.